Retinoic acid stimulates plasminogen activator inhibitor 2 production by blood mononuclear cells and inhibits urokinase-induced extracellular proteolysis

Abstract

Retinoids have been shown to modulate several functions of mononuclear phagocytes. We investigated the in vitro effect of all-trans-retinoic acid (ATRA) on the production of two major fibrinolytic components, urokinase-type plasminogen activator (u-PA) and PA inhibitor 2 (PAI-2), by human blood mononuclear cells (MNC). ATRA caused a dose-dependent (range 0.01-10 μM) accumulation of PAI-2 antigen and activity into the cell culture medium, with a maximal increase (about 5-fold over control) at a concentration of 1-10 μM. Similarly, a dose-dependent increase in PAI-2 antigen was observed in cell extracts upon ATRA stimulation. Northern blot analysis showed a parallel increase in the amount of PAI-2 mRNA in ATRA-treated cells. Time-course experiments with 1 μM ATRA showed enhanced PAI-2 mRNA expression as early as 2 h, reaching a maximum at 4-6 h and then declining at 18-24 h, and a time- dependent increase in PAI-2 antigen in the cell culture medium. At variance with PAI-2, u-PA was not influenced by the drug. To establish whether ATRA- induced changes influenced the fibrinolytic process, we evaluated the effect of MNC stimulated with ATRA on u-PA-induced degradation of diluted plasma clots. ATRA-treated cells markedly inhibited clot lysis induced by low concentrations of u-PA. The effect was due to enhanced extracellular PAI-2 accumulation since it was observed with conditioned medium from ATRA-treated cells; it was abolished by the addition of neutralizing anti-PAI-2 antibodies and was negligible when single-chain t-PA was used instead of u-PA. Since monocyte/macrophage-mediated, plasminogen-dependent extracellular proteolysis has been proposed as an important mechanism of tissue damage in several inflammatory states, our findings might contribute to better explain the anti-inflammatory properties of retinoids.